Search

Previous diffusion tensor imaging (DTI) studies indicate that impaired microstructural integrity of the normal-appearing white matter (NAWM) is related to cognitive impairment in cerebral small vessel disease (SVD). This study aimed to investigate whether quantitative T2 relaxometry is a suitable imaging biomarker for the assessment of tissue changes related to cognitive abnormalities in patients with SVD. 39 patients and 18 age-matched healthy control subjects underwent 3 T magnetic resonance imaging (MRI) with T2-weighted multiple spin echo sequences for T2 relaxometry and DTI sequences, as well as comprehensive cognitive assessment. Averaged quantitative T2, fractional anisotropy (FA) and mean diffusivity (MD) were determined in the NAWM and related to cognitive parameters controlling for age, normalized brain volume, white matter hyperintensity volume and other conventional SVD markers. In SVD patients, quantitative T2 values were significantly increased compared to controls (p = 0.002) and significantly negatively correlated with the global cognitive performance (r= –0.410, p = 0.014) and executive function (r= –0.399, p = 0.016). DTI parameters did not correlate with cognitive function. T2 relaxometry of the NAWM seems to be sensitive to microstructural tissue damage associated with cognitive impairment in SVD and might be a promising imaging biomarker for evaluation of disease progression and possible effects of therapeutic interventions. [ABSTRACT FROM AUTHOR]

Purpose: Auditory functional MRI (fMRI) often uses silent inter‐volume delays for stimulus presentation. However, maintaining the steady‐state of the magnetization usually requires constant delays. Here, a novel acquisition scheme dubbed "pre‐Saturated EPI using Multiple delays in Steady‐state" (SEPIMS) is proposed, using spin saturation at a fixed delay before each volume to maintain steady‐state conditions, independent of previous spin history. This concept allows for variable inter‐volume delays and thus for flexible stimulus design in auditory fMRI. The purpose was to compare the signal stability of SEPIMS and conventional sparse EPI (CS‐EPI). Methods: The saturation module comprises two non‐selective adiabatic saturation pulses. The efficiency of the saturation and its effect on the SEPIMS signal stability is tested in vitro and in vivo. Results: Data show that SEPIMS yields the same signal stability as CS‐EPI, even for extreme variations between inter‐volume delay durations. However, dual saturation pulses are required to achieve sufficiently high saturation efficiency in compartments with long T1 values. Importantly, spoiler gradient pulses after the EPI readout have to be optimized to avoid eddy‐current‐induced image distortions. Conclusion: The proposed SEPIMS sequence maintains high signal stability in the presence of variable inter‐volume durations, thus allowing for flexible stimulus design. [ABSTRACT FROM AUTHOR]

Background: In epilepsy patients with focal cortical dysplasia (FCD) as the epileptogenic focus, global cortical signal changes are generally not visible on conventional MRI. However, epileptic seizures or antiepileptic medication might affect normal-appearing cerebral cortex and lead to subtle damage.Purpose: To investigate cortical properties outside FCD regions with T2 -relaxometry.Study Type: Prospective study.Subjects: Sixteen patients with epilepsy and FCD and 16 age-/sex-matched healthy controls.Field Strength/sequence: 3T, fast spin-echo T2 -mapping, fluid-attenuated inversion recovery (FLAIR), and synthetic T1 -weighted magnetization-prepared rapid acquisition of gradient-echoes (MP-RAGE) datasets derived from T1 -maps.Assessment: Reconstruction of the white matter and cortical surfaces based on MP-RAGE structural images was performed to extract cortical T2 values, excluding lesion areas. Three independent raters confirmed that morphological cortical/juxtacortical changes in the conventional FLAIR datasets outside the FCD areas were definitely absent for all patients. Averaged global cortical T2 values were compared between groups. Furthermore, group comparisons of regional cortical T2 values were performed using a surface-based approach. Tests for correlations with clinical parameters were carried out.Statistical Tests: General linear model analysis, permutation simulations, paired and unpaired t-tests, and Pearson correlations.Results: Cortical T2 values were increased outside FCD regions in patients (83.4 ± 2.1 msec, control group 81.4 ± 2.1 msec, P = 0.01). T2 increases were widespread, affecting mainly frontal, but also parietal and temporal regions of both hemispheres. Significant correlations were not observed (P ≥ 0.55) between cortical T2 values in the patient group and the number of seizures in the last 3 months or the number of anticonvulsive drugs in the medical history.Data Conclusion: Widespread increases in cortical T2 in FCD-associated epilepsy patients were found, suggesting that structural epilepsy in patients with FCD is not only a symptom of a focal cerebral lesion, but also leads to global cortical damage not visible on conventional MRI.Evidence Level: 21 TECHNICAL EFFICACY STAGE: 3 J. MAGN. RESON. IMAGING 2020;52:1783-1789. [ABSTRACT FROM AUTHOR]

Purpose: The variable flip angle method derives T1 maps from radiofrequency‐spoiled gradient‐echo data sets, acquired with different flip angles α. Because the method assumes validity of the Ernst equation, insufficient spoiling of transverse magnetization yields errors in T1 estimation, depending on the chosen radiofrequency‐spoiling phase increment (Δϕ). This paper presents a versatile correction method that uses modified flip angles α' to restore the validity of the Ernst equation. Methods: Spoiled gradient‐echo signals were simulated for three commonly used phase increments Δϕ (50°/117°/150°), different values of α, repetition time (TR), T1, and a T2 of 85 ms. For each parameter combination, α′ (for which the Ernst equation yielded the same signal) and a correction factor CΔϕ(α, TR, T1) = α′/α were determined. CΔϕ was found to be independent of T1 and fitted as polynomial CΔϕ(α, TR), allowing to calculate α′ for any protocol using this Δϕ. The accuracy of the correction method for T2 values deviating from 85 ms was also determined. The method was tested in vitro and in vivo for variable flip angle scans with different acquisition parameters. Results: The technique considerably improved the accuracy of variable flip angle–based T1 maps in vitro and in vivo. Conclusions: The proposed method allows for a simple correction of insufficient spoiling in gradient‐echo data. The required polynomial parameters are supplied for three common Δϕ. Magn Reson Med 79:3082–3092, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Conventional MRI for brain tumor diagnosis employs T2-weighted and contrast-enhanced T1-weighted sequences. Non-enhanced T1-weighted images provide improved anatomical details for precise tumor location, but reduced tumor-to-background contrast as elevated T1 and proton density (PD) values in tumor tissue affect the signal inversely. Radiofrequency (RF) coil inhomogeneities may further mask tumor and edema outlines. To overcome this problem, the aims of this work were to employ quantitative MRI techniques to create purely T1-weighted synthetic anatomies which can be expected to yield improved tissue and tumor-to-background contrasts, to compare the quality of conventional and synthetic anatomies, and to investigate optical contrast and visibility of brain tumors and edema in synthetic anatomies. Conventional magnetization-prepared rapid acquisition of gradient echoes (MP-RAGE) anatomies and maps of T1, PD and RF coil profiles were acquired in comparable and clinically feasible times. Three synthetic MP-RAGE anatomies (PD T1 weighting both with and without RF bias; pure T1 weighting) were calculated for healthy subjects and 32 patients with brain tumors. In healthy subjects, the PD T1-weighted synthetic anatomies with RF bias precisely matched the conventional anatomies, yielding high signal-to-noise (SNR) and contrast-to-noise (CNR) ratios. Pure T1 weighting yielded lower SNR, but high CNR, because of increased optical contrasts. In patients with brain tumors, synthetic anatomies with pure T1 weighting yielded significant increases in optical contrast and improved visibility of tumor and edema in comparison with anatomies reflecting conventional T1 contrasts. In summary, the optimized purely T1-weighted synthetic anatomy with an isotropic resolution of 1 mm, as proposed in this work, considerably enhances optical contrast and visibility of brain tumors and edema. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate whether maps of quantitative T1 (qT1) differences induced by a gadolinium‐based contrast agent (CA) are better suited than conventional T1‐weighted (T1w) MR images for detecting infiltration inside and beyond the peritumoral edema of glioblastomas. Conventional T1w images and qT1 maps were obtained before and after gadolinium‐based CA administration in 33 patients with glioblastoma before therapy. The following data were calculated: (i) absolute qT1‐difference maps (qT1 pre‐CA ‐ qT1 post‐CA), (ii) relative qT1‐difference maps, (iii) absolute and (iv) relative differences of conventional T1w images acquired pre‐ and post‐CA. The values of these four datasets were compared in four different regions: (a) the enhancing tumor, (b) the peritumoral edema, (c) a 5 mm zone around the pathology (defined as the sum of regions a and b), and (d) the contralateral normal appearing brain tissue. Additionally, absolute qT1‐difference maps (displayed with linear gray scaling) were visually compared with respective conventional difference images. The enhancing tumor was visible both in the difference of conventional pre‐ and post‐CA T1w images and in the absolute qT1‐difference maps, whereas only the latter showed elevated values in the peritumoral edema and in some cases even beyond. Mean absolute qT1‐difference values were significantly higher (P < 0.01) in the enhancing tumor (838 ± 210 ms), the peritumoral edema (123 ± 74 ms) and in the 5 mm zone around the pathology (81 ± 31 ms) than in normal appearing tissue (32 ± 35 ms). In summary, absolute qT1‐difference maps—in contrast to the difference of T1w images—of untreated glioblastomas appear to be able to visualize CA leakage, and thus might indicate tumor cell infiltration in the edema region and beyond. Therefore, the absolute qT1‐difference maps are potentially useful for treatment planning. [ABSTRACT FROM AUTHOR]

The detection of cortical malformations in conventional MR images can be challenging. Prominent examples are focal cortical dysplasias (FCD), the most common cause of drug‐resistant focal epilepsy. The two main MRI hallmarks of cortical malformations are increased cortical thickness and blurring of the gray (GM) and white matter (WM) junction. The purpose of this study was to derive synthetic anatomies from quantitative T1 maps for the improved display of the above imaging characteristics in individual patients. On the basis of a T1 map, a mask comprising pixels with T1 values characteristic for GM is created from which the local cortical extent (CE) is determined. The local smoothness (SM) of the GM‐WM junctions is derived from the T1 gradient. For display of cortical malformations, the resulting CE and SM maps serve to enhance local intensities in synthetic double inversion recovery (DIR) images calculated from the T1 map. The resulting CE‐ and/or SM‐enhanced DIR images appear hyperintense at the site of cortical malformations, thus facilitating FCD detection in epilepsy patients. However, false positives may arise in areas with naturally elevated CE and/or SM, such as large GM structures and perivascular spaces. In summary, the proposed method facilitates the detection of cortical abnormalities such as cortical thickening and blurring of the GM‐WM junction which are typical FCD markers. Still, subject motion artifacts, perivascular spaces, and large normal GM structures may also yield signal hyperintensity in the enhanced synthetic DIR images, requiring careful comparison with clinical MR images by an experienced neuroradiologist to exclude false positives. [ABSTRACT FROM AUTHOR]

Background and Purpose Methods Results Conclusions In acute ischemic stroke (AIS) due to large‐vessel occlusion (LVO), the relationship between cerebral oxygen extraction fraction (OEF) as the hallmark of the ischemic penumbra and leptomeningeal collateral supply is not well established. We aimed to investigate the relationship between pial collateralization and tissue oxygen extraction in patients with LVO using magnetic resonance imaging (MRI).Data from 14 patients with anterior circulation LVO who underwent MRI before acute stroke treatment were analyzed. In addition to diffusion‐weighted imaging and perfusion‐weighted imaging (PWI), the protocol comprised sequences for multiparametric quantitative blood‐oxygen‐level‐dependent imaging for the calculation of relative OEF (rOEF). Pial collateral supply was quantitatively assessed by analyzing the signal variance in T2*‐weighted PWI time series. Relationships between collateral supply, infarct volume, rOEF in peri‐infarct hypoperfused tissue, and clinical stroke severity were assessed.The PWI‐based parameter quantifying collateral supply was negatively correlated with baseline ischemic core volume and rOEF in the hypoperfused peri‐infarct area (p < .01). Both reduced collateral supply and increased rOEF correlated significantly with higher scores on the National Institutes of Health Stroke Scale (p < .05). Increased rOEF within hypoperfused tissue was associated with higher baseline (p = .043) and follow‐up infarct volume (p = .009).Signal variance‐based mapping of collaterals with PWI depicts pial collateral supply, which is closely tied to tissue pathophysiology and clinical and imaging outcomes. Magnetic‐resonance‐derived mapping of cerebral rOEF reveals penumbral characteristics of hypoperfused tissue and might provide a promising imaging biomarker in AIS. [ABSTRACT FROM AUTHOR]

Background: Multiparametric quantitative MRI (mp-qMRI) provides noninvasive, quantitative measurements sensitive to a variety of tissue properties. In brain tumors (BTs), longitudinal relaxation time (T1), effective transverse relaxation time (T2*), transverse relaxation time (T2), water content (H 2 O), and quantitative susceptibility (χ) give valuable insights into the microenvironment. To generate large multicenter datasets, protocols need to be short and implementable on any scanner. The goal of this work was to develop and validate an 8-min, 3T mp-qMRI protocol for BT patients solely using generalized pulse sequences (mGRE and EPI)., Methods: A protocol was developed and tested on a multicompartment phantom, 5 healthy subjects (mean age: 31.64 years), and 4 BT patients (mean age:39.5 years) . Phantom and healthy subject longitudinal relaxation time (T1) maps were compared to those obtained using 2 reference methods. The 5 healthy subjects were scanned on 3T MRI scanners at 2 different sites and the reproducibility between scanners was assessed by computing Coefficients of Variance (COV) maps, performing Bland-Altman analysis and t -tests. Clinical feasibility was tested on 4 BT patients., Results: T1 values obtained using the proposed mp-qMRI protocol agree with those obtained using the reference methods in volunteers (mean error = 8.94 ms) . The qMRI maps (T1, T2*, H 2 O, and χ ) of the volunteers showed good reproducibility between scanners with no significant differences for mean WM and GM qMRI values. WM and GM mean qMRI values agreed well with literature values. H 2 O gave the lowest COV and χ maps the highest., Conclusion: The proposed vendor sequence-based 3T mp-qMRI protocol gives interpolated, high resolution (1 mm isotropic) T1, T2*, H 2 O, and χ maps in 8 min of acquisition., Competing Interests: The authors have no conflicts of interest to report., (© The Author(s) 2024. Published by Oxford University Press, the Society for Neuro-Oncology and the European Association of Neuro-Oncology.)

Purpose: Aim of this study was to develop a reliable B 1 mapping method for brain imaging based on vendor MR sequences available on clinical scanners. Correction procedures for B 0 distortions and slice profile imperfections are proposed, together with a phantom experiment for deriving the approximate time-bandwidth-product (TBP) of the excitation pulse, which is usually not known for vendor sequences., Methods: The double angle method was used, acquiring two gradient echo echo-planar imaging data sets with different excitation angles. A correction factor C (B 1 , TBP, B 0 ) was derived from simulations for converting double angle method signal quotients into bias-free B 1 maps. In vitro and in vivo tests compare results with reference B 1 maps based on an established in-house sequence., Results: The simulation shows that C has a negligible B 1 dependence, allowing for a polynomial approximation of C (TBP, B 0 ). Signal quotients measured in a phantom experiment with known TBP reconfirm the simulation results. In vitro and in vivo B 1 maps based on the proposed method, assuming TBP = 5.8 as derived from a phantom experiment, match closely the reference B 1 maps. Analysis without B 0 correction shows marked deviations in areas of distorted B 0 , highlighting the importance of this correction., Conclusion: Double angle method-based B 1 mapping was set up for vendor gradient echo-echo-planar imaging sequences, using a correction procedure for slice profile imperfections and B 0 distortions. This will help to set up quantitative MRI studies on clinical scanners with release sequences, as the method does not require knowledge of the exact RF-pulse profiles or the use of in-house sequences., (© 2023 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Previous diffusion tensor imaging (DTI) studies indicate that impaired microstructural integrity of the normal-appearing white matter (NAWM) is related to cognitive impairment in cerebral small vessel disease (SVD). This study aimed to investigate whether quantitative T 2 relaxometry is a suitable imaging biomarker for the assessment of tissue changes related to cognitive abnormalities in patients with SVD. 39 patients and 18 age-matched healthy control subjects underwent 3 T magnetic resonance imaging (MRI) with T2-weighted multiple spin echo sequences for T 2 relaxometry and DTI sequences, as well as comprehensive cognitive assessment. Averaged quantitative T 2 , fractional anisotropy (FA) and mean diffusivity (MD) were determined in the NAWM and related to cognitive parameters controlling for age, normalized brain volume, white matter hyperintensity volume and other conventional SVD markers. In SVD patients, quantitative T 2 values were significantly increased compared to controls (p = 0.002) and significantly negatively correlated with the global cognitive performance (r= -0.410, p = 0.014) and executive function (r= -0.399, p = 0.016). DTI parameters did not correlate with cognitive function. T 2 relaxometry of the NAWM seems to be sensitive to microstructural tissue damage associated with cognitive impairment in SVD and might be a promising imaging biomarker for evaluation of disease progression and possible effects of therapeutic interventions.